1. Field of the Invention
The present invention relates to a light conductor, a lighting apparatus and a liquid crystal display, and more particularly, relates to the light conductor, the lighting apparatus and the liquid crystal display suitable for a display section of a small electronic apparatus such as a PDA (Personal Digital Assistant).
The present application claims priority of Japanese Patent Application No. 2001-136950 filed on May 8, 2001, which is hereby incorporated by reference.
2. Description of Related Art
A liquid crystal display differs from a luminescent display such as CRT (Cathode Ray Tube) display, PDP (Plasma Display Panel) display and EL (Electro Luminescence) display. The liquid crystal of the liquid crystal display is not luminescent. In the liquid crystal display, characters and images are displayed by adjusting a transmission amount of light from a specific light source.
Liquid crystal displays are divided into two types: a transmission liquid crystal display and a refection liquid crystal display.
In the transmission liquid crystal display, a surface light source such as a fluorescent lamp and an EL is provided on the back of transmission liquid crystal display elements as a light source (back light).
In the reflection liquid crystal display, the display uses surrounding light reflected off a reflecting plate to display data. There are advantages in this type of display because no back light is needed and consumption of power is small. Further, in a well-lit place in direct sunshine, though the clarity of the luminescent display or the transmission liquid crystal display deteriorates, the reflection liquid crystal display is more clear. Therefore, the reflection liquid crystal display is currently used for the popular PDA or mobile computer.
However, since the reflection liquid crystal display uses the surrounding light for the display, display luminance depends on surroundings and the display is not operable in darkness, i.e., night. Particularly, in a reflection liquid crystal display using a color filter, the problem is more severe and strong surrounding light is necessary in comparison with a monochrome liquid crystal display. Though, to solve this problem, a half reflection liquid crystal display using a half mirror has been implemented. But, the method of manufacturing the half mirror is complicated, the light efficiency is low and the display quality is not good. Thus, a solution to the above problem is using a lighting apparatus to light the liquid crystal display when it is dark.
Conventionally, a liquid crystal display, as shown in FIG. 23, is provided with a lighting apparatus 10 and a liquid crystal panel 20. The lighting apparatus 10 is provided with a light source 11 and a light conductor 12. The light source 11 is a fluorescent lamp or a like and supplies light P1 to the light conductor 12. The light conductor 12 is made of polycarbonate resin or the like and is provided with an incident surface portion 12a, a prism surface portion 12b and an outgoing surface portion 12c. The light P1 from the light source 11 is input from the incident surface portion 12a and is reflected off the prism surface portion 12b. Reflected light P2 is output from the outgoing surface portion 12c. Reflected light P3 is input from the outgoing surface portion 12c and is output from the prism surface portion 12b to a viewpoint of an observer.
The liquid crystal panel 20 is provided with a polarizing plate+compensating plate 21, a glass substrate 22, a color filter 23, liquid crystal 24, a reflecting plate 25 and a glass substrate 26. Further, the color filter 23 is formed on the glass substrate 22, and the reflecting plate 25 is formed on the glass substrate 26. The liquid crystal panel 20 receives the reflected light P2, performs control corresponding to a display screen and reflects the reflected light P2 so as to output the reflected light P3 to the light conductor 12. The liquid crystal panel 20 also reflects external incident light received through the light conductor 12 from the viewpoint of an observer by the reflecting plate 25 so as to output the reflected light.
FIG. 24A and FIG. 24B are detailed view showing the light apparatus 10 in FIG. 23. FIG. 24A is a view indicated by an arrow A of the lighting apparatus 10 in FIG. 23. FIG. 24B is a sectional view along a line c-c in FIG. 24A. FIG. 24A also shows a view indicated by the arrow A of the liquid crystal panel 20.
In the lighting panel 10, as shown in FIG. 24A, a string of prisms are formed on the prism surface portion 12b of the light conductor 12. The string of prisms are provided with propagation portions 12m, 12m . . . , 12m for propagating the light P1 and refection portions 12n, 12n . . . 12n for reflecting the propagated light P1 which are repeatedly formed in a density corresponding to a pixel density of a display screen of thee liquid crystal panel 20. An included (inclination) angle θ is set between a direction vertical to a repetition direction of a string of prisms and the incident surface portion 12a. As shown in FIG. 24B, in the string of prisms, a repetition pitch P, a width W between the reflection portions 12n and a depth D of the repetition portion 12n are set.
FIG. 25 is a view showing the lighting apparatus 10 viewed from the arrow A when the included angle θ in FIG. 24A is set to 0°. In the lighting apparatus 10, the included angle θ is set to 0°, and the string of prisms are repeatedly formed in a vertical direction to the incident surface portion 12a. The light source 11 is provided with a fluorescent lamp 11a, a length Z of an emission portion is shorter than a length of the incident surface portion 12a in order to make a frame of the liquid crystal display small.
FIG. 26 is a view showing the light apparatus 10 indicated by the arrow A when the fluorescent lamp 11a in FIG. 25 is emitting.
As shown in FIG. 26, the light P1 is input into the incident surface portion 12a from the fluorescent lamp 11a and is propagated in the light conductor 12. In this case, since the length Z of the emission portion of the fluorescent lamp 11a is shorter than the length of the incident surface portion 12a, there are areas to which no light is propagated and a rectangular dark portion B1 and a rectangular dark portion B2 are generated at both sides of the light conductor 12. Widths of the rectangular dark portion B1 and the rectangular dark portion B2 reduce in proportion to a distance from the incident surface portion 12a caused by diffraction of the light P1.
FIG. 27 is a view showing another conventional liquid crystal display. The same numerals are applied to the same elements in FIG. 23.
The liquid crystal display is provided with a lighting apparatus 10A different from the lighting apparatus 10 in FIG. 23 instead of the lighting apparatus 10. The lighting apparatus 10A is provided with a light conductor 12A of which a repetition direction of a string of prisms is different (namely, included angle θ≠0°) instead of the light conductor 12 in FIG. 23.
FIG. 28 is a view showing the lighting apparatus 10A viewed from the arrow A, and the same numerals are applied to the same elements in FIG. 25.
In the lighting apparatus 10A, a string of prisms are repeated in a direction inclined to the incident surface portion 12a. 
FIG. 29 is a view showing the light apparatus 10A indicated by the arrow A when the fluorescent lamp 11a in FIG. 28 is emitting. FIG. 30 is a detailed view showing a dark portion C and a dark portion D in FIG. 29.
As shown in FIG. 29, the light P1 is input into the incident surface portion 12a from the fluorescent lamp 11a and is propagated in the light conductor 12A. In this case, since the length Z of the emission portion of the fluorescent lamp 11a is shorter than the length of the incident surface portion 12a, there are areas to which no light is propagated and a dark portion C1 and a dark portion C2 are generated in the repetition direction of the string of prisms.
In other words, as shown in FIG. 30, since most of the light P1 of the fluorescent lamp 11a propagates in the repetition direction W of the string of prisms (namely, included θ+90°), dispersion light P11 of the light P1 propagates in the repetition direction W and dispersion light 12P transmits through an end surface. Therefore, the dark portion C generates only at one corner contact with the incident surface portion 12a of the light conductor 12A. Further, since dispersion light P13 and dispersion light P14 propagate in the repetition direction W and dispersion light P15 and dispersion light P16 transmit through an end surface, the dark portion generates from another corner contact with the incident surface portion 12a of the light conductor 12A in the repetition direction of the string of prisms.
However, there are following problems in the conventional liquid crystal displays.
In the liquid crystal display shown in FIG. 23, as shown in FIG. 26, the rectangular dark portion B1 and the rectangular dark portion B2 generate in the light conductor 12, and further there is a case in that moire stripes generate according to the pixel density of the liquid crystal panel 20. Therefore, there is a problem in that a display quality of the liquid crystal panel 20 remarkably deteriorates.
Also, in the liquid crystal display shown in FIG. 27, as shown in FIG. 29, the dark portion C and the dark portion D generate. There is no problem about the dark portion C by setting the dark portion out of a display area. However, since the dark portion D generates in the display area, there is a problem in that a display quality remarkably deteriorates. To solve these problems, it is considered that the length Z of the emission portion of the fluorescent lamp 11a is longer than the length of the incident surface portion 12a. However, when the length Z of the emission portion is longer than the length of the incident surface portion 12a, a whole length of the fluorescent lamp 11a becomes long, there are problems in that a configuration of the liquid crystal display becomes large and it is difficult to make a frame small.
Further, Japanese Patent Application Laid-Open No. 2000-19330 discloses a technique for preventing the moire stripes. In this technique, since a repetition direction of a string of prisms to prevent the moire stripes is considered about only a square pixel unit and is not considered about a RGB cell, there is a possibility in that moire stripes generate under a specific display such as whole blue display, whole red display or whole green display. Therefore, the consideration is not satisfied.